1. Field of the Invention
The present invention relates to a semiconductor device and a method for manufacturing the semiconductor device. In particular, it relates to a semiconductor device capable of decreasing a resistance between an electrode of a semiconductor element and an electrode of a lead and a method for manufacturing the semiconductor device.
2. Description of the Related Art
In the recent semiconductor market, demanded are semiconductor devices which can operate at high speed and have high throughput while consuming low power during operation. In order to satisfy such opposed needs, miniaturization of a circuit of a semiconductor device has been advancing. In addition, in order to effectively utilize supplied power, the inner resistance (for example, on-resistance) of the entire semiconductor device has been decreased.
One citable example of semiconductor devices is a transistor package including a FET used for switching and amplifying a current. In this transistor package, electrodes on a semiconductor element and electrodes of leads are electrically connected by multiple wires formed of a conductive metal, such as gold (Au) or aluminum (Al).
Examples of inner resistances may include a resistance component of the wring member connecting the semiconductor element and the lead, and a resistance component of a connection between the wiring member and each electrode. In general, a metal wire is used as the wiring member. However, the resistance of this metal wire occupies a nonnegligibly-large portion in the inner resistance value of the entire semiconductor device. Accordingly, if the resistance of the metal wire could be decreased even when the metal wire is used, the resistance component of the connection between the electrode of the semiconductor element and the electrode of the lead can be also decreased.
A possible measure to achieve this is to thicken the metal wire or to increase the number of the metal wires. However, a technically-difficult problem is caused due to short-circuit of adjacent metal wires or limitations on the number of and space for the wires to be attached. In particular, when the wire is thickened, the wire becomes difficult to bend. Thereby, a loop height thereof becomes higher. Furthermore, there is not so much flexibility in designing in relation to a distance between the electrode on the semiconductor element and the electrode of the lead. For this reason, to secure a space for the bending of the metal wire, the total height of the semiconductor device has to be consequently increased.
On the other hand, as a method for lowering the resistance value of the metal wire per se, it is possible to change a metal material forming the metal wire to a material with a lower resistance than that of gold (Au) or aluminum (Al). However, this method can hardly be employed, because usable metals are limited from the viewpoint of cost and reliability in jointing portions is not so high.
As one method for solving such problems, Japanese Patent No. 3240292 and Japanese Patent Application Publication No. 2002-76195 disclose a semiconductor device in which an electrode of a semiconductor device and an electrode of a lead are electrically connected by using a plate-like conductive metal material in order to lower a resistance of the entire semiconductor device. That is, this method allows an expansion of the cross-sectional area of a current channel between the electrode of the semiconductor element and the electrode of the lead. Thereby, the resistance between the electrode and the lead can be lowered.
However, in the invention disclosed in Japanese Patent No. 3240292, a gate electrode of the semiconductor element and the lead are connected by the metal wire. Thus, for the above-described reason, there is a limitation of decreasing the inner resistance of the semiconductor device.
In addition, the invention disclosed in Japanese Patent No. 3240292 and Japanese Patent Application Publication No. 2002-76195 mainly focus on use of the plate-like conductive metal wire to decrease the resistance of the semiconductor device, and, for this reason, do not describe at all how to decrease the resistance of a semiconductor device which uses a metal wiring material other than such plate-like metal material. Furthermore, in Japanese Patent No. 3240292 and Japanese Patent Application Publication No. 2002-76195, there is no description of a method for further decreasing the resistance when the plate-like metal material is used.
The present invention has been made in view of the foregoing problems. Accordingly, an object of the present invention is to provide a semiconductor device that is highly reliable and easy to manufacture as well as that can further decrease an inner resistance without an increase in the size of the semiconductor device, and a method for manufacturing the semiconductor device.